The present invention is directed to a method for the through-connection of multiplex signals via cross connectors.
In a digital connecting network of a synchronous digital hierarchy (SDH) according to the CCITT recommendations G.707, G.708 and G.709, the digital signals to be transmitted are inserted into specific data blocks, referred to as synchronous containers C-n, by positive filling at the input node to the synchronous network. Each container is supplemented to form a virtual container VC-n by attaching an auxiliary signal (POH). The virtual containers are periodically transmitted. The first byte of a virtual container is indicated by a pointer whose chronological position is defined in the transmission frame. As a rule, the virtual container of a higher hierarchy level serves as transmission frame. Together with the pointer allocated to it, a virtual container VC-n forms a tributary unit TU-n. A plurality of tributary units having the same structure can in turn be combined to form a tributary unit group TUG-n. In the aforementioned CCITT recommendations, only the tributary unit groups TUG-21 for the 1.5 Mbit/s hierarchy (USA) and the TUG-22 for the 2 Mbit/s hierarchy that, among other things, is standard in Europe are expressly cited. Tributary unit groups of a higher order may be seen in the figures of the CCITT recommendation G.709.
The CCITT recommendation is used for the definition of higher tributary unit groups TUG-31 and TUG-32 in a disclosure of France Telecom for CCITT having the title "Considerations about G.709 Multiplexing Structure" presented at the conference in Geneva, Jun. 19-30, 1989.
The French proposal for the formation of a synchronous transmission signal STM-1 is shown in FIG. 1. Various plesiochronic signals H11 through H22 (M therein denotes Mbit/s) indicated at the right-hand side can be combined via various multiplexing paths to form the synchronous transmission signal STM-1. The arrow directions in FIG. 1 thereby respectively indicate the direction to a more complex multiplex signal or, respectively, to a multiplex signal of a higher level. The same multiplexing path must be employed at both sides of a digital connection. The multiplexing paths for signals of the 1.5 Mbit/s hierarchy (USA) are shown in the upper half and the multiplexing paths of the 2 Mbit/s hierarchy are shown in the lower half. The STM-1 frame has a period of 8 KHz and consists of 270 columns and 9 rows, corresponding to 270.times.9 bytes. Directly or indirectly via further pointers, the frame identifier word thereby defines the position of all required pointers of the data blocks to be transmitted.
What are referred to as cross connectors (CC) are provided in the trunk line network (FIG. 2), these cross connectors (CC) making it possible to connect multiplex signals over various connecting paths. The cross connectors can thereby undertake the through-connection with a mechanical or electronic switching matrix network. This can be a synchronous space switching matrix network, a synchronous time slot switching matrix network, a time slot-coupled space switching matrix network or a combination thereof. Telephone subscribers having dedicated connections or switched connections (F +W) are essentially referred to herein as subscribers, and have access to the trunk line network either directly or via a switching level.
Whereas through-connections or call transfers can be undertaken in every hierarchy level (multiplexing level) in the plesiochronic hierarchy, no interfaces are standardized in the synchronous hierarchy between the individual hierarchy levels below the STM-1 signal of 155.520 Mbit/s, this initially making a through-connection and call transfer impossible.
Desired switching levels in the 2 Mbit/s hierarchy should be provided for the data blocks TU-12, TU-22, TUG-22, TU-31, TUG-31, AU-31 and AU-4. In the 1.5 Mbit/s hierarchy, the corresponding switching levels would be desirable for data blocks TU-11, TU-21, TUG-21, TU-32, TUG-32, AU-32 and AU-4. With the exception of the switching level AU-4 (administrative units that, however, are not the subject matter of the invention), the switching levels for the 2 Mbit/s hierarchy and for the 1.5 Mbit/s hierarchy require different equipment.